Long-standing debate: are we really getting less violent than our forebears?

A well-known American psychologist claims that the modernization of western societies has driven down the rates of war casualties, implying that human violence has decreased. Not so fast… conclude two new studies.

Two recently published scientific papers claim that the statistical reasoning behind the idea – proposed a few years ago by well-known American psychologist Steven Pinker– that humans have become less violent owing to modernity and social progress is flawed. According to these studies, we are probably neither more nor less violent than before.

The question of how we compare to our forebears in terms of violence has been in the limelight since 2011, when Harvard University’s Pinker, in his best-selling book The Better Angels of our Nature: Why Violence Has Declined. He theorized that History had witnessed a civilizing process, as a result of the modernisation of government and state, that now made us less violent than ever before.

Pinker based his provocative conclusion on historical records of war casualties – and more specifically, on the observation that the proportion of the population succumbing to violent conflicts has clearly declined in time. According to this metric, even the 20th century, apart from a few “bumps” such as two World Wars and a Holocaust, was far less violent than more ancient epochs, says Pinker.

His book has been widely acclaimed. But there has also been some serious criticism. Not least from well-known American-Lebanese scholar and statistician Nassim Taleb, who has stated that Pinker’s underlying statistics are “naive”.

In the first of the latest papers, published last October in the journal Current Anthropology, anthropologists Dean Falk (Florida State University) and Charles Hildebolt (Washington University) recall Pinker’s line of thought: “psychologist Steven Pinker cites mean ratios of war (battle) deaths suffered annually per 100,000 individuals as evidence for concluding that people who live in [modern] states are less violent than those who live or lived in ‘hunting, gathering and horticultural societies in which our species spent most of his evolutionary history’”.

But these authors claim instead that Pinker’s use of war casualties per capita to sustain his hypothesis of decreasing violence – numbers which “are blind to actual population sizes” – masks the fact that population size is precisely what affects the rates of violence, rather than a particular type societal organization. In other words, it cannot be ignored that population size has a so-called “scaling effect” on casualties rates.

To understand why, picture this: ancient human communities might be typically composed of a few hundreds of individuals (maybe a few thousands), whereas modern nations count millions (even billions) of citizens. So clearly, the former type would be more deeply impacted by any conflict that killed just a few of its members than the latter ever will be by conflicts whose toll reaches in the hundreds of thousands. Citizens of populous nations are, by design so to speak, less individually exposed to conflict violence simply because they are hugely more numerous.

To prove their point, Falk and Hildebolt compare annual war deaths for 24 humans groups not structured as a state and for 19 and 22 countries that respectively fought in WWI and WWII, this time taking into account the actual population sizes of each of these human communities.

The second study aiming to contradict Pinker’s theory was published this December in the journal Proceedings of the National Academy of Sciences (PNAS). In it, University of Notre Dame anthropologist Rahul Oka and his colleagues also asked themselves if there was a simple, mathematical explanation for the decrease in the proportion of people who die in battle today with respect to past times. For this, they analysed historical data from more than 400 battles, some of which date back more than 2,500 years.

They too identify a scaling effect of population size on war deaths. “The probability of any random individual being involved in any conflict or being a casualty of a conflict decreases with growing populations and complexity”, they write. Their results suggest, that the historical trends invoked by Pinker can be better explained by the fact that, as populations grow exponentially, per capita war casualties go down, a law that “seems to hold across societies, regardless of (…) the type and nature of institutions within any society past and present”.

Pinker does not agree. According to a news piece published in the journal Science, when asked to comment on the PNAS study, he replied that those results are no more than a “statistical gimmick”. Oka, in turn, rebutted this by saying that his team was simply trying to put historical and modern violence in the adequate context – and that we are “as peaceful as we’ve always been”. Or as violent.

Ana Gerschenfeld works as a Science Writer at the Science Communication Office at the Champalimaud Neuroscience Programme